In this article
- What they are and how they are transmitted
- Genetic diseases
- The different types
- Genetic test yes or no
What are hereditary diseases and how are they transmitted
When deciding to have a child, the desire of every mom and dad is that the unborn child be healthy. However, it can sometimes happen that a child is born with a genetic disease although the parents are not affected and are in excellent health. This is the case with hereditary diseases.
As Francis Collins, director of the National Human Genome Research Institute said, "Everything in medicine, with the possible exception of trauma, is genetic in nature." In fact, all of us are carriers of mutations, present in the genome, which can cause hereditary diseases. Mutations may have no effect on our health, but they can pose a risk if the partner was a healthy carrier of the same disease.
A hereditary disease is certainly genetic since it is a disease whose cause is a mutation in one or more genes. A hereditary disease is transmitted from parents to children through DNA following precise rules of transmission, as is the case with the color of the eyes or the blood type.
As we have seen, hereditary diseases are genetic diseases. Even the latter are not all the same and are divided into:
- Chromosomal diseases: they occur when there is an alteration in the number of chromosomes or when one or more chromosomes are damaged, as in the case of Down syndrome;
- Monogenic diseases: when there is a mutation of a single gene;
- Multifactorial genetic diseases: result of the combination of gene alterations, lifestyle and environmental factors, as in the case of Alzheimer's or diabetes.
The different types of inherited disease transmission
As the World Health Organization reminds us, the ways of inheriting genetic diseases are different from each other.
When the disease can be inherited without distinction from mom or dad and there is a 50% chance that the baby will be born sick, as with achondroplastic dwarfism or Huntington's chorea, let's talk about autosomal dominant inheritance.
L'autosomal recessive inheritance instead it occurs when both parents are healthy carriers of the genetic mutation and the disease is transmitted in 25% of cases. In this situation there is a 50% chance that the baby will be a healthy carrier and a 25% chance that it will be born completely healthy.
Another case is that ofrecessive X inheritance which occurs when a healthy woman carrying the altered gene is expecting a son. The disease is transmitted to the child in 50% of cases, while if it is a female daughter, only the condition of a healthy carrier will be transmitted with a 50% probability. This is the case of haemophilia, Duchenne muscular dystrophy and favism.
Finally, the rarest case, that ofdominant X inheritance, in which it is enough that only one copy of the gene is mutated (therefore only in one parent) for the disease to occur. However, diseases of this type are extremely rare.
How is a hereditary disease diagnosed
Thanks to prenatal diagnostics it is now possible to identify this type of disease before childbirth. For some years it has been possible to carry out fetal DNA tests starting from the tenth week of pregnancy to highlight the presence of chromosomal abnormalities such as trisomies 13, 18 and 21. Furthermore, thanks to the use of amniocentesis it is possible to study the DNA of the fetus by performing a multiple genetic screening that will allow to detect any genetic diseases.
In our country they are esteemed over 6000 hereditary diseases. The most frequent are:
- Mediterranean anemia: 1 in 2500 children
- Cystic fibrosis: 1 child in 2700
- Fragile X syndrome: 1 child in 4000
- Congenital deafness: 1 in 4000 children
There is also another way to "play early" and that is to undergo a genetic test before pregnancy, in order to check for any incompatibilities.
Genetic test: yes or no?
Couples who want a child can contact their doctor to find out about the risks deriving from genetic anomalies. The comparison with a specialist is useful to understand if it is appropriate to carry out a genetic test or not, especially based on family medical history, as also recommended by the US Department of Health. There are cases in which a genetic test is strongly recommended, such as when in the family (brothers, uncles, cousins) there are sick people or healthy carriers of an identified genetic disease.
The test analyzes the DNA of both parents to find out if are healthy carriers of one or more hereditary diseases, or if they have genetic characteristics that could favor the onset of a disease, so as to know the risk of the child being born sick.
Genetic tests are usually performed at affiliated health facilities only for people at higher risk (in the family there are sick people or healthy carriers) than the general population. For low-risk couples, the choice is subjective and voluntary.
Genetic testing, Centre for Desease Control and prevention https://www.cdc.gov/genomics/gtesting/genetic_testing.htm
Council of Europe adopts protocol on genetic testing for health purposes, European Journal of Human Genetics https://www.nature.com/articles/ejhg200984
Genetic Disorders, National Human Genome Research Institute https://www.genome.gov/For-Patients-and-Families/Genetic-Disorders
Preconception health, Ministry of Health http://www.salute.gov.com/portale/donna/dettaglioContenutiDonna.jsp?lingua=Del Paeseno & id = 4474 & area = Salute% 20donna & menu = birth
- Prenatal diagnostic tests
- Amniocentesis: what it is and when it is performed
- Villocentesi: what it is and when to do it
- prenatal diagnosis
- test at screening